In any transportation industry, reliable communications systems are mandatory for avoiding serious, if not catastrophic, accidents. In the particular case of the railroads, the railroad central offices normally communicate through wired telecommunications links with a network of radio base stations, which are typically dispersed over very large geographical areas. The radio base stations in turn maintain wireless communication links with locomotives, service vehicles, and wayside systems operating within the base station coverage areas.
In designing and operating a communications system for a transportation industry, a number of different constraints must be addressed. In the railroad industry, for example, a reliable and efficient communications system must be capable of handling different types of information, including data transmitted from the railroad central office and wayside systems to the locomotive on-board computers, as well as voice transmissions between train crews and the central office.
One particularly critical application for wireless communications is in interoperability positive train control systems. A positive train control (PTC) system is a system that is designed for the express purpose of preventing train-to-train collisions, over-speed derailments, incursions into established work zone limits, and the movement of a train through a switch left in the wrong position. A PTC system is “interoperable” if it allows locomotives of a host railroad and a tenant railroad to communicate with and respond to the PTC system, while supporting uninterrupted movements over property boundaries. Interoperability PTC (IPTC) systems have been mandated for some railroads under the Rail Safety Improvement Act of 2008 (Public Law 110-432 of 2008).
Any wireless system communication system used in an IPTC system must not only meet the requirements and goals of the Rail Safety Improvement Act of 2008, but also must meet the transmission band requirements mandated by the Federal Communications Commission (FCC), including, for example, those related to frequency band allocation, channel width and spacing. Moreover, in addition to meeting all of the government imposed requirements, an IPTC system must also meet all of the engineering demands placed on any system being deployed in the harsh railroad operating environment.